1. Field of the Invention
The present invention relates to an apparatus or method for providing protection to a generator.
2. Description of the Background Art
A generator capability curve from a manufacture gives the generator rating at rated coolant temperature. When operating at temperatures that differ from rated, the capability of the generator may be demonstrated by other capability curves. Automobile applications are sensitive to changes in temperature conditions as the capability of a generator varies significantly with temperature conditions. In such automobile applications, ambient temperature and ventilation affect the performance of a generator as the generator operates within an engine compartment where the generator and an internal combustion engine heat ambient air. Besides, the amount of heat issued by a generator tends to increase because a need for increased electric energy has led an increase in generator capability.
In such automobile applications, air-cooled generators have traditionally been used. Within an engine compartment, the use of ambient air as coolant involves potential difficulty to keep a temperature condition of a generator within an acceptable range for normal generator operation. This has led extensive investigation of the use of liquid coolant for automobile applications. A liquid-cooled AC generator has been proposed, which is driven by an internal combustion engine and associated with a radiator and a pump. Liquid coolant is cooled at the radiator and supplied by the pump to cool the generator parts. One example of such liquid-cooled generator is shown in JP P2000-125599. According to this prior art, temperature sensors are arranged for measuring inlet temperature of liquid coolant to an AC generator and outlet temperature thereof from the generator, respectively. When a difference between measures of inlet and outlet coolant temperatures falls outside of an acceptable range for steady normal operation, operation of the generator is limited to protect it. While the prior art limiter implementation can properly protect the generator, it does not account for a temperature condition of the generator upon failure of the temperature sensors.
It is thus seen to be desirable to monitor a temperature condition of a generator without temperature sensors.